Market research has established that consumers select bread and similar bakery products based upon their fresh, soft texture. Staling is perceived by the development of a firm, dry texture which becomes noticeable within one or two days after baking, and results in a loss of product acceptability. Monoglycerides and other surfactant compounds are added to bread to achieve improved softness. Surfactants usage results in softer bread, but they do not materially affect the rate of bread firming.
Bread staling or firming is due primarily to changes, which occur in the starch fraction. The firming of bread crumb cannot be attributed to changes in moisture content, since the moisture content of one and six day old bread is essentially the same when the product is packaged to prevent moisture loss. Yet, the bread texture becomes increasingly firmer on storage, and is usually considered unacceptable after the fourth day. Evidence shows that amylose and amylopectin starch fractions retrograde or crystallize during bread storage to form a firm, dry texture. Starch makes up about 70 percent of the dry weight of bread, and evidence indicates that some of the textural changes, which are observed on staling, are due to crystallization of the starch components.
Since bread staling or firming is believed to be caused by crystallization of gelatinized starch, it would appear that these textural changes could be modified or inhibited by using starch hydrolyzing enzymes to fragment the starch polymers, thus reducing the degree of interaction or firming on storage. Attempts to use commercially available enzyme preparations, such as heat stable bacterial alpha-amylase enzyme have not met with success because the degree of enzyme action has been too difficult to control. Either the degree of enzyme action has been inadequate with little or no improvement in bread texture, and anti-firming properties, or when enough enzyme is added to obtain a softer texture, failures arise due to the formation of a very tacky, gummy bread crumb with a loss of load volume and destruction of bread quality.
It is the object of this invention to develop a heat stable enzyme system, which can be used to provide a controlled degree of alpha-amylase activity to inhibit the firming of bread and other bakery products, thus achieving a longer product storage life without loss of quality.